Method for reproducing images of a solid photocatalyst with an oxidizing agent

ABSTRACT

The present invention relates to an embodiment of the invention disclosed in U.S. Pat. No. 3,152,903 in which a radiation image is reproduced by exposing a carrier bearing a photocatalyst and an oxidizing agent to radiation to reduce a portion of the oxidizing agent present to a free metal defining a latent image which serves as a catalyst site for the subsequent development reaction of a reducing agent and the non-reduced oxidizing agent.

ilnited States Patent Shepard et al.

[541 METHOD FOR REPRODUCING IMAGES OF A SOLID PHOTOCATALYST WITH ANOXIDIZING AGENT [72] Inventors: Joseph W. Shepard, St. Paul; Benjamin L.

Shely, White Bear Lake, both of Minn.

[73] Assignee: Minnesota Mining and Manufacturing Company, St. Paul,Minn.

[ Notice: The portion of the term of this patent subsequent to Feb. 25,1986, has been disclaimed.

[22] Filed: Nov. 29, 1968 211 Appl. No.: 780,283

Related US. Application Data [63] Continuation of Ser. No. 517,469, Dec.29, 1965, Pat. No. 3.429.706. which is a continuation of Ser. No.221,329, Sept. 4, 1962, abandoned, which is a continuation-in-part ofSer. No. 809,927, Apr. 30, 1959, Pat. No. 3,152,903.

[151 3,655,383 [451 *Apr. 11, 1972 Primary Examiner-Norman G. TorchinAssistant Examiner-John L. Goodrow Att0mey-Kinney, Alexander, Sell,Steldt & Delahunt [57] ABSTRACT The present invention relates to anembodiment of the invention disclosed in US. Pat. No. 3,152,903 in whicha radiation image is reproduced by exposing a carrier bearing aphotocatalyst and an oxidizing agent to radiation to reduce a portion ofthe oxidizing agent present to a free metal defining a latent imagewhich serves as a catalyst site for the subsequent development reactionof a reducing agent and the non-reduced oxidizing agent.

3 Claims, No Drawings METHOD FOR REPRODUCING IMAGES OF A SOLIDPHOTOCATALYST WITH AN OXIDIZING AGENT This application is a continuationof our copending application Ser. No. 517,469, filed Dec. 29, 1965, nowUS. Pat. No. 3,429,706 which is a continuation of our copendingapplication Ser. No. 221,329, filed Sept. 4, 1962, now abaondoned, whichis a continuation-in-part of our prior application Ser. No. 809,927,filed Apr. 30, 1959, now US. Pat. No. 3,152,903.

The present invention relates to a novel and useful radiation-sensitivesystem. In one aspect the invention relates to the permanentreproduction of images or patterns on a surface by irradiation. inanother aspect the invention relates to a new light-sensitivecomposition and to a reproduction surface or sheet made from suchcomposition. In still another aspect the invention relates to a new andnovel photographic process in which an image is reproduced directlywithout the conventional developing step.

Numerous processes are known for the light reproduction of images andfor copying. One of the more common and typical of such processes isthat known as the silver halide process. This process requires exposureof a sensitive film or paper to the light or image source followed by aseparate step of wet developing of the image on the film or paper.

Another typical process is known as electrophotography, and this processdepends upon the presence of a photoconductive material in the film orprinting paper. As in the silver halide process, this process requires aseparate step of developing of the image. If fixing is necessary ordesirable, fixing may be done by a dry process, such as by heat.

The silver halide process and similar processes are considered moresensitive than the electrophotographic process. The disadvantage of thesilver halide process, however, is the rather involved developingprocedure. On the other hand, the disadvantage of theelectrophotographic process is the low sensitivity thereof to thereproduction of images. Most of the processes require a separate step inaddition to the developing step for the fixing of the image so that uponexposure to normal light conditions the image will not fade or thebackground will not darken. It is much to be desired, therefore, toprovide a simpler process than the above with elimination of theirdisadvantages. It has been discovered that certain materials have acatalytic effect upon reactions when activated by irradiation. Thisphotocatalytic effect is taken advantage of in accordance with thepresent invention.

An object of this invention is to provide a novel light-sensitivecomposition or combination of components.

Another object of this invention is to provide a novel process forgraphic reproduction or copying of printed matter and the like.

Another object of this invention is to provide a process which directlyreproduces the image or directly copies upon exposure to the object tobe reproduced and does not require a separate step of developing.

Still another object of this invention is to provide a lightsensitivecombination of components of increased sensitivity for the graphicreproduction of images and the like.

Still another object of this invention is to provide a dry process forgraphic reproduction.

Still another object of this invention is to provide a process fordirectly reproducing transparencies.

Yet another object of this invention is to provide a novel copy-paper orfilm.

Another object is to provide a new photographic transparency film.

Still another object of this invention is to provide a dry graphicreproduction process which is receptive to a braoder light spectrum thanheretofore possible.

Another object of this invention is to provide a new imagereproducingcomposition which can be developed and fixed in a single operation.

Still another object of this invention is to provide a new technique forpermanently fixing or stabilizing a reproduced image.

Various other objects and advantages will become apparent to thoseskilled in the art from the accompanying description and disclosure.

According to this invention, the radiation-sensitive system comprises animage-forming combination of components or composition and a separateradiation-sensistive catalyst or photocatalyst chemically different fromthe image-forming composition. The radiation-sensitive system is usuallyin a dry or even anhydrous form and is supported by or is a part of asuitable inert carrier or sheet. The carrier sheet containing theradiation-sensitive system is then exposed to an image source or lightsource, and the image or pattern to be copied is reproduced eitherimmediately upon exposure or upon subsequent development. In someinstances, fixing or inactivation of the radiation-sensitive system isrequired so that upon viewing the reproduction, the image or reproducedmatter will not fade or the background will not darken.

The image-forming or reactive components of the system are in the formof an irreversible oxidation-reduction reaction combination which iscapable of initiation into reaction or of catalyzation by electrontransfer thereto from the photocatalyst. The oxidation-reductionreaction combination or composition comprises two solid phases; aseparate solid phase comprising an oxidizing agent and another separatesolid phase comprising a reducing agent. During exposure to radiation,the oxidizing agent reacts with the reducing agent whereby areproduction of the image or pattern results, which reproduction may belatent (invisible) or visible. Any redox combination of an oxidizingagent and a reducing agent having a negative-free energy under theexposure or development conditions suffices as the image-forming orreactive composition.

In one embodiment of the invention, the reaction of theoxidation-reduction combination upon exposure produces a product orproducts having a change in color or reflectance resulting in avisiblereproduction. In another embodiment, the reaction product or products ofthe reaction of the oxidation-reduction combination upon exposure arenot visible (latent image) but are made to react further with each otheror with other materials in a subsequent development step to produce avisible reproduction by a change in color or reflectance. In bothembodiments, the image-forming composition is substantially dry whenexposed, and reaction is effected at least partially at the time ofexposure under exposure conditions which are usually ambient conditions.Exposure may be effected at somewhat elevated temperatures, such as 50C. Subsequent reactions, if necessary, are effected by heating above theexposure temperature or by wetting the exposed redox combination withwater.

In addition to the image-forming combination or compositionabove-described, the radiation-sensitive system requires a third solidphase comprising, as a radiation-sensitive catalyst, a relativelynonreactive material which is not the same as the oxidizing agent or thereducing agent and can be activated into the transfer or release ofelectrons upon exposure to irradiation having a wave length below 5microns, preferably below 1 micron, such as actinic light, X-rays orgamma rays. Electrons are transferred from the catalyst to theoxidationreduction combination, usually to the oxidizing agent as theelectron acceptor, which electrons initiate or catalyze the reaction.

The radiation-sensitive system may comprise an admixture of the abovethree separate solid phases or may comprise separate layers of each, orlayers of a combination of any solid phases, in any order. Theradiation-sensitive catalyst phase may be applied as a layer bonded to asuitable carrier or inert substrate. Upon the catalyst layer is affixedthe image-forming combination in the form of a single layer comprisingan admixture of components or in the form of two separate adjacentlayers of each of the components. Any one or all of the components ofthe radiation-sensitive system may also comprise, or be impregnated in,the carrier. Any one of the reactive components may be included with thecatalyst layer and the other reactive component included in a separatelayer adjacent and in contact with the catalyst layer.

Although inactivation of the image reproduction system is not requiredin all instances, depending upon the components of the system or type ofirradiation source used, in many instances an inactivation or fixingoperation is desirable or necessary Where the irradiation source isx-rays or gamma rays, visual observation of the image will not becarried out in the presence of such rays, and, therefore, inactivationmay not be necessary. On the other hand, where the type of irradiationsource is actinic light and the visual image reproduction is to beobserved in the presence of such light, inactivation is required in mostinstances. Inactivation is carried out by inactivating the image-formingcomposition such as by removing or complexing at least one of theunreacted components, by inactivating the photocatalyst, or by the useof a combination of these methods.

In order to maintain the oxidizing agent and the reducing agent asseparate solid phases, at least one of these reactive components isadmixed with a material or binder which is incompatible or immisciblewith that component or with the other component or with a secondmaterial or binder used with the other component. ln applying thepresent combination to an inert substrate, such as paper, the metalcontaining catalyst is applied or affixed to the surface, such as withan organic resin or binder. Then one of the components of theoxidation-reduction combination is admixed with an organic solvent ordiluent containing dissolved therein an organic resin as a binder, whichadmixture is applied as a continuous layer over the catalyst layer anddried to form a solid layer. Upon this layer is applied the otherreactive component from a solution thereof, the solvent of whichsolution is substantially immiscible with, but bondable to, the organiclayer containing the other reactive component. Since most of theoxidizing agents and reducing agents are water-soluble, this latterlayer may be applied from an aqueous solution containing dissolvedtherein a water-soluble binder to form a continuous layer when dried.There are various techniques which will become obvious to those skilledin the art for maintaining the reactive components and catalyst inseparate phases and in a nonreacted condition while in admixture or incontact with each other while departing from the scope of thisinvention.

The reactive components of the radiation-sensitive composition are inactual contact or in mutually interreactive relationship with eachother, but are physically distinct from each other. The catalyst issimilarly in such close relationship with the reactive components as tobe capable of transferring electrons to at least one of the componentswhen the catalyst is activated by radiation.

As previously stated, the image-forming combination includes both anoxidizing agent and a reducing agent. The oxidizing agent in thiscomposition is usually the image former, but not necessarily. Eitherorganic or inorganic oxidizing agents may be employed as the oxidizingcomponent of the image-forming combination. The preferred oxidizingagents comprise the metal salts, either inorganic or organic. Suitablemetal salts include the salts of silver, mercury, lead, gold manganese(in the form of the permanganate), nickel, tin, chromium, platinum andcopper. Examples of typical nonmetal salt oxidizing agents include thenonmetal organic salts and dyes comprising the tetrazolium salts, suchas tetrazolium blue (33 dianisole-bislA (3,4 diphenyl) tetrazoliumchloride) and red (triphenyl-tetrazolium chloride) and diphenylcarbazone, and Genacryl Red 68, a methine dye (CI 48020).

When zinc oxide is used as a photocatalyst, as will hereinafter bediscussed, molecules or ions with reduction potential below oxygen inthe electromotive series are useful as the oxidizing agent in eitherneutral or acid media. Thus, the salts of the reducible metal ions, Ag,Hg, Pb, Au, Pt and MnO can be used as the oxidizing agent with zincoxide as the photocatalyst upon irradiation. in basic media, moleculesor ions below zinc in the electromotive series can be used as theoxidizing agent when zinc oxide is used as the photocatalyst. Thus, thereducible metal ions, Ni Sn, Pb" and Cu, are suitable in salt form asthe oxidizing agent with zinc oxide as a photocatalyst on exposure toirradiation.

When the above metal salts are used as the oxidizing agent, an organicnonmetal complexing agent may be used which will complex with the metalion of the above metal salts. Thus, carbazone can be reduced to thecarbazide and an image formed by complexing a metal ion with thecarbazide. Also, additives may be used in combination with the oxidizingagent to change the character and tonal value of the image. Images oftenassume a darker and more dense tone when the metal ion of the oxidizingagent is complexed with another material. For example, the density of asilver image is increased by the use of a small amount of an organiccomplexing additive, such as an acid amide as, for example, formamide oracetamide, and phytic acid. Similarly, the density of a gold image isincreased by use of acetamide.

The reducing agents of the image-forming composition which arechemically different from and physically separate from the oxidizingagents are organic reducing compounds, such as the oxalates, formates,substituted and nonsubstituted hydroxylamine and substituted andnonsubstituted hydrazine, ascorbic acid, aminophenols and the mono anddihydric phenols. The oxalates and formates are usually in the form ofsalts of the alkali earths and alkali metals, such as sodium, lithiumand potassium. A preferred oxalate salt is sodium oxalate. A preferredformate is sodium formate. Examples of substituted hydroxylaminesinclude phenyl hydroxylamine and benzyl hydroxylamine. An example of anaminophenol is Metol (l,4-rnethyl-p-aminophenol) and Elon(N-methyl-paminophenol sulfate); an example of a substituted hydrazineis phenyl hydrazine. Suitable mono and dihydric phenols include lonol(2,6-ditertiary-butyl-4-methyl-phenol), hydroquinone and catechol.

As previously stated, some of the oxidizing agents work best in acidicor basic media. Suitable acids which can be employed in admixture withthe oxidizing agent and reducing agent as part of the image-formingcomposition include the carboxylic acids, such as oxalic acid andstearic acid. The basic media may be provided in the image-formingcomposition by the inclusion therein of an organic or inorganic base,such as ammonium hydroxide or sodium acetate, or any salt of a strongbase and weak acid.

The selection of the particular oxidizing agent to be used with aparticular reducing agent is, of course, determined in one aspect by theability of either one or both of the compounds in their reacted form toshow a change in light value (a change in color or reflectance), or toreact with another compound resulting in a change in light value. Theoxidationreduction potential (E.) for the reaction between the oxidizingagent (electron acceptor) and the reducing agent (electron donor) mustbe positive under the conditions of reaction. This can be calculatedfrom the standard electrode potentials (E) for the half cells.Preferably, the oxidation-reduction potential (E.) for the reaction isat least +0.1 volt.

As previously stated, the light-sensitive catalyst or photocatalyst is aseparate solid phase which may be combined with the ingredients in theimage-forming composition or may form a separate layer or impregnated inthe carrier. The photocatalyst is a material which will transferelectrons when activated by a radiation wave length below 5 microns.Such photocatalysts comprise both inorganic photoconductors andnonphotoconductors. Among the inorganic photoconductors which may beusedare zinc oxide, indium oxide, zinc sulfide, cadmium sulfide andselenium. Of the photoconductors, the N-type is preferred, such as zincoxide. Inorganic nonphotoconductors which act as photocatalysts are thepolyvalent metal oxides including titanium dioxide and antimonytrioxide. Of both the photoconductors and nonphotoconductors abovedescribed, the white materials are preferred to assure a whitebackground.

It has also been found that certain fluorescent or phosphorescent metalcompounds are also useful as In place of the ethylenediamine (C H N H,)and ammonia of the above compounds, such coordinating groups asguanidine, azido and nitrite may be used. Other readily reducible anionswhich may be used in place of those of the peroxydisulfate of the abovecomplexes include tetrathionate, selenate and perchlorate.

A simple test may be used to determine whether or not materials have aphotocatalytic effect. The material in question is mixed with an aqueoussolution of silver nitrate and no reaction should take place in theabsence of light. The mixture is then exposed to light at the same timethat a control sample of an aqueous solution of silver nitrate alone isexposed to light, such as ultraviolet light. If the mixture darkensfaster than the silver nitrate alone, the material is a photocatalyst.If, however, a reaction does take place in the absence of light, thematerials should be coated out separately on a flat surface using asuitable binder in accordance with the procedure described herein. Acontrol sheet is also made for comparison. The test is carried out onthe sheets as described above.

The irradiation source is an important feature of the present invention.Ultraviolet light is one of the best radiation sources, and all of thephotocatalytic materials are sensitive thereto. Incandescent light is afair source of ultraviolet light. Fluorescent light is a better sourceof ultraviolet light. The photocatalysts are not usually sensitive tothe entire actinic light range but may be made so by the use of a dyesensitizer, such as eosin, Seto FlavinT, Thioflavin, uranine,erythrosin, phosphine R, orthochrome P, Vasoflavin and dicyanine A.Radiation by x-rays or gamma rays is also effective in exciting thephotocatalyst to transfer electrons.

The binding agent used to bind the image-forming composition and thephotocatalyst to the carrier medium is also an important feature of thepresent invention. In general, these binders should be translucent ortransparent so as not to interfere with the transmission of lighttherethrough. The preferred binders for the reactive components andcatalyst are organic materials, such as solid polymers and resins.Suitable organic resins and copolymers include a copolymer of butadieneand styrene sold on the open market as Pliolite, polystyrene,chlorinated rubber, polyvinylchloride, nitrocellulose, rubberhydrochloride, polyvinylbutyral, polyethyleneglycol, carbowax, polyamideresin sold as Zytel-6l, hydroxyethyl cellulose, methyl cellulose andpolyvinylpyrrolidone. The polartype binders which are water oralcohol-soluble are useful with one of the reactive components, such asbinders including polyethyleneglycol, polyvinylbutyral, polyamide resinand carbowax and polyvinylpyrrolidone. These binders may be removed bydissolving the binder with water or alcohol and thus removing theoxidizing and/or reducing agent. This inactivates the carrier to furtherexposure to light as will be hereinafter discussed. The nonpolar bindersor water or alcohol insoluble organic binders are useful with the otherreactive component or both reactive components. These binders includepolystyrene, chlorinated rubber, rubber hydrochloride,polyvinylchloride, nitrocellulose and Pliolite.

Any of these binders may be used for the catalyst phase, but thenonpolar binders are preferred. The binders may also be admixed and usedin admixture for layer formation.

The carrier material or support upon which the photocatalyst andimage-forming composition are deposited may be any suitable inertbacking of sufficient strength and durability to satisfactorily serve asa reproduction. The carrier or support may be in the form of sheets,ribbon, roll or other suitable form for supporting the reproduction ofthe image. The carrier may comprise wood pulp paper, rag content paper,various synthetic plastics, such as cellulose acetate and polyethyleneterephthalate (Mylar) in the form of film, cotton or wool cloth, metalfoil and glass plate. The preferred form of the backing or carriermaterial is a thin sheet which is flexible and durable.

An example of a suitable white paper containing theirradiation-sensitive system of this invention comprises zinc oxide as aphotocatalyst, silver nitrate as the oxidizing agent and image-formingmaterial, and sodium formate or sodium oxalate as the reducing agent,all of which are bonded to the paper as a continuous uniform layer. Aslurry is formed of these materials with an immiscible organic binderand diluent and coated on a wood pulp-type paper in a thickness of about4 mils. Approximately equal proportions of the components of the systemare used. A resin such as Pliolite (copolymer of butadiene and styrene)is useful as the binder since it securely adheres the components to thepaper and to each other. Another method of construction is to apply anadmixture of a zinc oxide and silver nitrate to the paper first in abouta 2-mil thickness with a suitable binder, such as Pliolite, followed bya separate layer of the reducing agent sodium formate in an aqueoussolution of a suitable water-soluble binder such as carbowax.

A negative film or transparency (developed) as a master is applied tothe surface of the above paper containing the image-forming compositionand catalyst. The film is then exposed to actinic light (500 lumens) forabout 1 to 15 seconds. The paper and film are then removed from thepresence of the actinic light, and film removed from the paper. Thepaper contains a reproduced black image (Ag) on the film, even thoughthe paper has been dry throughout the procedure. When zinc oxide isomitted from the above process, no visible image is formed in 30 secondsof exposure. If in the above system the reducing agent is omitted, therate of image formation is considerably slower unless the backing or thebinder itself contains a reducing agent or is in itself a reducingagent.

In the above typical system using zinc oxide, ultraviolet light has beentheorized to raise the electrons of the zinc oxide into its conductionband in accordance with the following equation:

ZnflO, light ZnQO' (8) Zn O is zinc oxide crystal; Zn is the excitedelectron; O is the hole (absence of electron). The silver ion of theoxidizing agent then apparently removes the electron from the zinc oxideconduction band in accordance with the following equation:

Zn Ag -Zn Ag (9) The hole created by the removal of the electron fromthe zinc oxide conduction band migrates to the surface and recombineswith an electron from the organic reducing agent (electron donor) inaccordance with the following equation:

01 HCOO O" CO (g) H (10) It may not be necessary that the electronactually be raised to the conduction band by the light, such as in zincoxide or other photoconductive materials. Irradiation may sufficientlyactivate the electron of the photocatalyst such that it is in an excitedstate and loosely held to the photocatalyst. In such a condition, theelectron is easily transferred to the oxidizing agent (electronacceptor) of the oxidation-reduction system to initiate an irreversiblereaction by electron transfer. This is the case with nonphotoconductors,such as the fluorescent materials, the metal complexes and thenonphotoconductive metal oxides.

The probable theory for the action of the metal complexes asphotocatalysts is that the metal ion can exist in more than oneoxidation state, a nonionic ligand and an oxidizable anion. Theirradiation of the complexes involves excitation of electrons in theanions to higher energy levels by the absorption of radiation wavelengths. The electrons thus excited become trapped in association withmetal ions. The electrons, however, tend to return to their originalstate when irradiation ceases. If an oxidizing agent, an easilyreducible compound, is present, the electrons are available by transferto the oxidizing agent and initiation of the irreversibleoxidation-reduction reaction occurs.

Mixtures of the various components of the system may be used as well asthe single components. Thus, mixtures of two or more photocatalysts maybe used. Also, mixtures of two or more oxidizing agents or two or morereducing agents may be used without departing from the scope of thisinvention. Even mixtures of binders may be used.

The oxidizing agent and reducing agent are usually used in substantiallystoichiometric proportions. If desired, an excess of the oxidizing agentmay be used without departing from the scope of this invention. Theweight ratio of the image-forming composition, i.e. the combination ofoxidizing agent and reducing agent, to photocatalyst is between about10:1 and about 1:10; preferably 2:1 to 1:2. The binder is used inasufficient amount to effectively bind the various ingredients to thecarrier surface. Generally, the weight ratio of binder to the materialto be bound is between about 2:1 to about 1:5.

The thickness of the image-reproducing system on the carrier will varybetween about 0.5 and about 8 mils. In case separate layers for thereactive components and the photocatalyst are used on the carrier base,the total thickness will be within the above range and the thickness ofeach layer will be about 0.5 mil to about 4 mils. The thickness of theinert carrier base or support, when in the form of a flexible sheet, isusually between about 5 and about 30 mils.

The exposure time will vary to a considerable extent and will dependprimarily upon the type and intensity of light or irradiation source,the sensitivity of the oxidation-reduction reaction, and upon thesensitivity of the photocatalyst. In general, the time of exposure willvary between about 0.001 of a second and about minutes. Generally, thereproduction requires not more than about seconds exposure.

Normally, it is the oxidizing agent that reproduces the image. Forexample, a dark material may turn light upon reaction or a lightmaterial may turn dark. Also, a white material or colorless material mayturn a color upon reaction or vice versa. Any change in the reflectionof light from the surface as a result of the reaction between thereducing agent and the oxidizing agent constitutes a change in lightvalue which causes a visual reproduction of the image, which reactionmay be effected simultaneously with exposure or in a subsequentdeveloping step.

As previously stated, in one embodiment of this invention the imageafter exposure is latent under ambient and normal conditions. In otherwords, there is no visible image formed upon exposure which is effectedat a temperature not higher than about 50 C., usually at ambientconditions, even in the presence of the photocatalyst, although areaction has taken place. In this embodiment, the exposed system issubsequently treated by heating above 50 C, or by wetting with water tocause further reaction. Upon further reaction, either the reducing agentor the oxidizing agent or some other reactive compound changes in lightvalue so as to reproduce the image in those areas where the initialreaction has taken place; for example, where the initial reactionproduces free metal in a small and invisible quantity which catalyzesthe subsequent reaction to form the image.

The source of this free metal is the oxidizing agent as disclosed above.The oxidizing agent accepts an excited electron from the exposedphotocatalyst according to reactions (8) and (9) above. Again the rateof image formation, here a latent image, is enhanced by the presence ofan electron donor (reducing agent) at the time of exposure. As shown byreactions (8) and (9) reduction of a portion of the oxidizing agent tothe metal proceeds by donation of electrons from the photocatalyst tothe oxidizing agent at the exposure time. The function of the reducingagent if present at the time of exposure is explained by reaction (10)above, i.e., the reducing agent serves to provide electrons forrecombining with the hole thus created. Thus, the reducing agent presentat the time of light exposure serves as an electron source for thephotocatalyst. The metal which is produced upon exposure of thephotocatalyst forms the latent image, the metal then serving to catalyzethe subsequent development reaction between the oxidizing agent and thereducing agent at the side of such metal to provide the developed,visible image. Thus, a carrier sheet bearing a photocatalyst and anoxidizing agent may be light exposed to reduce a portion of theoxidizing agent to a free metal defining a latent image, and this latentimage may be developed by treating the exposed sheet with a reducingagent, e. g., hydroquinone. The oxidizing agent may be applied to thecarrier sheet at any time prior to exposure. The oxidizing agent whichwas not reduced at the time of exposure reacts with the reducing agentadded after exposure in the presence of the free metal to provide thevisible image corresponding to the latent image. Preferably, prior tolight exposure there is also present on the carrier sheet a reducingagent, e.g., an oxalate, in a separate solid phase which in its role asan electron source for the photocatalyst aids in formation of the latentimage. A second reducing agent is then employed in the postexposure,development step which reacts with oxidizing agent to form additionalfree metal in the presence of latent image free metal catalyst.

The photocatalyst should be conditioned in the dark before exposure whenthe catalyst is sensitive to actinic light. Usually dark conditioning ofthe photocatalyst of l to 24 hours is desirable in such instances. Afterconditioning, the catalyst is not exposed to light prior to its exposurefor reproducing the image.

Preferred image-forming compositions comprise (oxidizing agent andreducing agent): silver nitrate and sodium formate or oxalate, coppersulfate and sodium formate, or sodium oxalate, silver saccharin andhydroquinone, silver saccharin and Metol or Elon, tetrazolium blue andsodium formate or sodium oxalate, silver behenate and lonol, diphenylcarbazone and sodium oxalate or sodium formate, silver nitrate or coppersulfate and sodium formate and benzene diazonium fluoroborate as astabilizer, gold chloride and sodium oxalate or sodium formate, and goldchloride and hydroquinone.

The image-forming combinations of this invention in dry condition arenot nonnally considered light-sensitive in the absence of thephotocatalyst. These reactive combinations, upon exposure to anultraviolet light source such as a mercury arc lamp (2,0004,000 lumens)for a period of time from 5 to 10 minutes, do not show any sensitivityto the light and are therefore considered normally latent under ambientconditions. Some sensitivity may be observed, darkening of thecomposition, upon prolonged exposure of several hours to an intenselight source with certain combinations, such as with silver nitrate anda reducing agent. In other combinations, such as with silver saccharinand a reducing agent, no sensitivity is observed even upon prolongedexposure to light when no photocatalyst is present. These redoxcombinations are in no way similar in sensitivity to the silver halideemulsion type of light-sensitive compositions or those which are aqueousor moist (in solution).

In addition to the above, the redox combinations may be divided into twoclasses, one class in which the redox combination results in areproduction of the image simultaneously with exposure (print outsystem), and the other class in which the visible reproduction is madeafter exposure by a separate developing step, such as by heating.

As previously stated, inactivation of the radiation-sensitive system isrequired where the reproduced image will be observed under the same orsimilar light conditions used during exposure or when the system doesnot require a subsequent development step, such as heating or wetting.However, where the light conditions of observation are not the same asunder exposure, such as exposure to X-rays or gamma rays or wherespecial development is required, no stabilization or inactivation of theimage-reproducing system may be necessary.

One method of inactivation is washing off one of the components of theimage-reproducing system after exposure. Washing may be effected withwater or any suitable solvent, such as an alcohol or a ketone. Forexample, a permanent copy of a photographic negative may be obtained bycoating out the photocatalyst, such as zinc oxide, in a water-insolublebinder, such as Pliolite, and coating either the oxidizing agent orreducing agent on this surface with a water-soluble binder, such aspolyethyleneglycol. After development of the image either at the time ofexposure or in a subsequent step, the water-soluble film containing oneof the reactive components can be washed off by holding under runningtap water for several seconds. The reproduced image remains on the zincoxide-Pliolite surface and is a permanent copy. By this method apermanent photographic print can be obtained in approximately 20seconds, including all of the operations for making the print.

Another method for inactivation of the image reproduction system is bythe use of heat in combination with the material capable of releasing anacid, i.e. either a Bronsted or Lewis classified acid, such as HCl, BFHF, PC1 and p-toluene sulfonic acid. In accordance with this procedure,metal ions that are above oxygen in the electromotive series, such ascopper, are used to deposit an image from a basic media directly uponexposure to the image source. The metal salt oxidizing agent, thereducing agent and a basic additive are coated with suitable binders ontop of a zinc oxide coated carrier. If separate layers are used for thereactive components, the layer containing the metal salt oxidizing agentwill also preferably contain the basic additive. Since metals aboveoxygen in the electromotive series do not deposit in neutral media, thelayer or layers forming the image-forming combination are neutralizedafter light development of the image therein which stabilizes the metalion of the metal salt oxidizing agent. This is accomplished by releasingan acid by a heat-sensitive reaction after exposure.

For example, the radiation-sensitive system is heated to a temperatureof about 100 to 250 C. A suitable composition that will release hydrogenchloride and thus neutralize the basic material upon heating is anadmixture of mnitrobenzenesulfonyl chloride (acid-releasing compound)and phloroglucinol. This admixture is added to the layer containing themetal salt oxidizing agent of the photosensitive sheet. This methodgives a dry reproduction, light-sensitive image system that does notrequire a development step and is heatinactivated to give a permanentstable copy. Other acidreleasing compounds include p-toluene sulfonicacid urea addition complex, p-acetamidobenzene diazonium fluoroborate,and m-chlorobenzene diazonium fluorophosphate.

Another method for releasing acids as a means of inactivation includesmoistening of the system with water which results in the release of anacid in the system as above. This type of operation does not requireheating. In this method of inactivation or fixing, diazoniumfiuoroborate is used alone and is combined on the top layer with amethanol or watersoluble polyamide binder. Included in this top layer,of course, is the metal salt oxidizing agent composition. The lowerlayer of this system is a photocatalyst dispersed in a nonwater-solublebinder, such as Pliolite. The reducing agent may be included in thelower layer or be in another separate intermediate layer using anonwater-soluble binder, but cannot be included in the top layer if thebinder is water-soluble. Upon wetting the top layer containing thewater-soluble binder with water, the fluoroborate decomposes, releasingBF of HF, thus neutralizing the basic media used in the image-formingcomposition and inactivating the composition to further sensitivity tolight. No heating is required. A variation of the above two types ofoperations is the inclusion in the layer containing the metal saltoxidizing agent and the acid former a compound that liberates water atlow temperatures, which water will react with the acid former toliberate the acid. A diazonium fluoroborate as the acid former willrelease BF upon heating to about C. in the presence of a hydrate,resulting in an inactivation system stable to further light sensitivity.

Another method of inactivation of the image reproduction systemconstitutes the chelation of the oxidizing agent or reducible metal ionby forming a very stable metal chelate with any of the unreacted metalions of the oxidizing agent. The chelating compound is combined in thebinder or layer containing the oxidizing agent. The chelating compoundmay also be used as a separate adjacent layer either above or below thelayer containing the oxidizing agent. The chelating compound may also beadmixed in a system where all of the components are mixed together witha single layer formation. In this method, the image reproduction systemis exposed to develop the image and then heated at a temperature ofabout 120 to 250 C. to form the metal chelate with the unreacted metalion of the oxidizing agent. The metal chelate formed must benonlight-sensitive. A suitable chelating agent which may be used whencopper is the metal ion of the oxidizing agent is salicylaldoxine. Thecopper-salicylaldoxine chelate formed upon stabilization of the systemis light colored and very stable. Another chelating agent isbenztriazole which may be used when silver is the metal ion of theoxidizing agent. Heating such a system to a temperature of about to 200C. results in a black image on a stable white background which is nolonger sensitive to light.

A simple test for determining whether the metal chelate isnonlight-sensitive is to expose the metal chelate to ultraviolet light.If the material does not darken after 5 minutes exposure, the chelatingagent is suitable as a means for inactivation of the system.

Inactivation of the image reproduction system may also be accomplishedby the application of pressure to the surface of the carrier. It hasbeen found that pressure will desensitize the photocatalyst, such aszinc oxide, as a result of which it is no longer light-sensitized. Thus,the sheet containing the image as a result of exposure may be passedthrough rolls which exert pressure upon the sheet. Another method is topass a bar under pressure across the surface of the sheet containing theimage. Generally, at least 500 pounds per square inch pressure must beapplied to the surface to deactivate the photocatalyst. It has beenfound that with zinc oxide, for example, passing a pencil or rod acrossthe image surface with exertion of heavy hand pressure will deactivatethe zinc oxide to further sensitization by actinic light. This type ofinactivation is that which inactivates the photocatalyst rather than theimageforming composition.

Still another method of inactivation is to separately bind thephotocatalyst and at least one of the reactive components on separateindependent sheets. The sheets are then firmly pressed together andexposed to light. Thereafter the sheets are separated and the image isformed on either the photocatalytic carrier or the image-formingcarrier, depending upon the type of image-forming composition used. Onemethod is to coat one sheet with a pressure-sensitive adhesivecontaining the image-forming combination, and the other sheet is coatedwith the catalyst and a conventional binder. The sheets are pressedtogether and form a sufficient bond such that electrons may transferfrom one sheet to the other. After exposure, the sheets are separated bypulling them apart. The two-sheet method has been found to be quitedistinctive in that a transparency or negative can be formed immediatelyupon exposure. For example, the image-forming combination which isusually transparent may be coated upon a transparent backing or carrier,such as Mylar film. The second sheet is coated with a pressure-sensitiveadhesive which contains a photosensitive catalyst in admixture therewithor which contains the photocatalyst dusted on the surface. The sheetsare pressed together and the combined sheets are then exposed to animage source, such as through a negative. After exposure, the sheets areseparated and a transparency is produced upon the Mylar film containingthe image-forming composition. As a modification of the above, theimage-forming compound, such as the oxidizing agent, is coated on thefirst sheet with a transparent binder. The second sheet is coated withan adhesive containing both the photocatalyst and the other component ofthe image-forming composition, such as the reducing agent. Various othercombinations as will become apparent from the above are within the scopeof this invention. The above methods of forming transparencies aresimple and inexpensive and are particularly adapted to use by theamateur photographer.

The system of the present invention may be particularly adaptable toamateur photography. In accordance with the present invention, acomposition of this invention is placed upon a paper backing in rollform and directly placed in the camera. The image is formed immediatelyupon exposure and the only remaining step in order to obtain a print isthe inactivation of the composition. This may be done by the amateurphotographer by removing the exposed print in the dark and washing withwater as above-described. When using zinc oxide as the photocatalyst,inactivation may also be achieved by using hand pressure with a pencilover the surface of the print. The camera itself can be constructed tohave the film pass through small pressure rollers to desensitize theprint. Other modifications or alterations are obvious for adaptation toconventional cameras.

The following Examples are offered as a better understanding of thepresent invention and are not to be construed as unnecessarily limitingthereto. In the Examples, the zinc oxide used was New Jersey ZincCompanys zinc oxide of the U.S.P.- 12 or Red Seal No. 9 type and wasprepared by the French process of burning zinc metal in air, and thetitanium dioxide was Mercks analytical reagent grade.

EXAMPLE I A dispersion of (42 parts by weight) photoconductive zincoxide and (three parts by weight) sodium oxalate (reducing agent) in asolution of 11 parts by weight) Pliolite, (23 parts by weight) acetone,(24 parts by weight) toluene was ballmilled for 12 hours. Thisdispersion was coated 4 mils thick on a transparent Mylar film as aflexible support and dried at room temperature with a subsequentdark-adapting period of 12 hours. A top layer, containing five parts byweight silver nitrate (oxidizing agent), 20 parts by weight ofwater-soluble binder material carbowax (20-M), and 75 parts water wascoated in the dark on the white zinc oxide layer in a thickness of about3 mils and allowed to air-dry in the dark. The dried sheet gave an imagein to seconds exposure to a mercury arc lamp (3,000 lumens). This sheetwas fixed by washing away'the unreacted silver nitrate along with thewater-soluble binder. The image of reduced silver clings to the surfaceof zinc oxide in Pliolite and remains intact with a white background onthe nonimage areas.

Substitution of a wood pulp paper as a support for the Mylar plasticfilm gave similar results to the above. Also, any commercial sun lampwill give a' satisfactory source of ultraviolet light for exposure.

Other water-soluble binders, such as polyvinylpyrrolidone, hydroxyethylcellulose and methyl cellulose, can be used in place of carbowax for thetop layer containing the oxidizing agent. Other normally water insolubleor nonwater-soluble organic binders, such as polystyrene andpolyvinylchloride, work equally well as binders for the photocatalyticlayer containing the reducing agent in place of Pliolite.

EXAMPLE [I A dispersion of (42 parts by weight) zinc oxide in (l l partsby weight) Pliolite, (three parts by weight sodium oxalate, (23 parts byweight) acetone and (24 parts by weight) toluene was ball-milled for 12hours. The zinc oxide and the sodium oxalate are immiscible with thePliolite and the solvent. This dispersion was coated 4 mils thick onMylar film as a flexible support and dried at room temperature with asubsequent dark-adapting period of 12 hours. An aqueous solutioncontaining dissolved therein 4 parts by weight copper sulfate, 20 partsby weight of water-soluble binder carbowax (20-M), one part by weight ofhexamethylenetetramine (basic media), and 75 parts water, was coated inthe dark on the zinc oxide layer to a thickness of about 2 mils andallowed to air-dry in the dark. The dried sheet gave a permanent imagein 30 seconds exposure to a mercury arc lamp (3,000 lumens). This sheetwas fixed by washing away the top layer along with water-soluble binderand basic media. The image sheet was stabilized by washing away thebasic media which was necessary for the oxidation-reduction reactionbetween the sodium oxalate and the copper sulfate.

EXAMPLE III A dispersion of 42 parts by weight of zinc oxide in l 1parts by weight of Pliolite, 23 parts by weight of acetone, 24 parts byweight of toluene and three parts by weight of sodium oxalate isball-milled for 12 hours. This dispersion is coated 4 mils thick on aMylar support and dried at room temperature with a subsequent darkadapting period of 12 hours. An imageforming layer containing 1 part byweight gold chloride, 24 parts by weight polyvinylpyrrolidone, and 75parts by weight methanol is coated to 3 mils and allowed to air dry inthe dark. This sheet is exposed to a mercury arc lamp for 20 secondswith the formation of a latent image. The exposed sheet is dipped in asolution of hydroquinone with an immediate visual development of theimage in the light-struck areas. This is an example of latent imageformation by light with subsequent visual development of the latentimage by an external reducing agent. The sheet is then washed to removethe unreacted image-forming material and water-soluble binder to give astable sheet.

EXAMPLE IV A dispersion of 42 parts by weight of zinc oxide in l 1 partsby weight of Pliolite, 23 parts by weight of acetone, and 24 parts byweight of toluene is ballmilled for 12 hours. This dispersion is coated4 mils thick on a Mylar support and dried at room temperature with asubsequent dark adapting period of 12 hours. An image-forming layercontaining 1 part by weight gold chloride, 24 parts by weightpolyvinylpyrrolidone, and 75 parts by weight methanol is coated to 3mils and allowed to air dry in the dark. This sheet is exposed to amercury arc lamp for 20 seconds with the formation of a latent image.The exposed sheet is dipped in a solution of hydroquinone with animmediate visual development of the image in the light-struck areas.This is an example of latent image formation by light with subsequentvisual development of the latent image by an external reducing agent.The sheet is then washed to remove the unreacted image-forming materialand watersoluble binder to give a stable sheet.

EXAMPLE V A dispersion of 42 parts by weight zinc oxide in l 1 pans byweight Pliolite, 23 parts by weight acetone, 24 parts by weight tolueneand three parts by weight sodium oxalate is ball-milled for 12 hours.This dispersion is coated 4 mils thick on a Mylar support and dried atroom temperature with a subsequent dark adapting period of 12 hours. Thecoated sheet is dipped in an alcoholic 3 percent solution of silvernitrate. The excess is wiped off and the sheet dried. The sheet isexposed to light through a transparency in a projection device. Novisible image is discernible. Subsequent to exposure, the sheet isdipped in an aqueous 1,4-methyl paramino-phenol sulfate (Elon) bath andthe latent image is developed in a second to a reflected optical densityof greater than 1.0.

sheet is exposed to light through a transparency in a projection device.No visible image is discernible. Subsequent to exposure, the sheet isdipped in an aqueous 1,4-methyl paraminophenol sulfate (Elon) bath andthe latent image is developed in a second to a reflected optical densityof greater than 1.0.

EXAMPLE VII A dispersion of 44 parts by weight of photoconductive Frenchprocess zinc oxide powder, 36 parts by weight of 30 percent by weight ofPliolite in toluene, three parts by weight of sodium formate, 30 partsby weight of acetone, and 4 X 10 grams of Phosphine R (C.I.46055) pergram of zinc oxide as a 2 percent by weight alcoholic solution isball-milled for 12 hours. The dispersion is coated 4 mils thick (wet) ona paper base and dried at room temperature with a subsequent darkadapting period of 12 hours. The exposed sheet is swabbed with a 2percent alcoholic solution of silver nitrate and allowed to dry. Thesheet is exposed via a projection transparency to a tungsten source. Thelight striking the surface is 100 foot candle seconds. Subsequent toexposure, a 1 percent solution of 2,2'-dinapthyl-para-phenylene-diamineis applied to the exposed sheet. The sheet is washed with a thioureastabilizer after a dense image is formed.

EXAMPLE VIII A dispersion of 44 parts by weight of photoconductiveFrench process zinc oxide powder, 36 parts by weight of 30 percent byweight of Pliolite in toluene, 30 parts by weight of acetone, and 4 X 10grams of Phosphine R (C.I.46055) per gram of zinc oxide as a 2 percentby weight alcoholic solution is ball-milled for 12 hours. The dispersionis coated 4 mils thick (wet) on a paper base and dried at roomtemperature with a subsequent dark adapting period of 12 hours. Theexposed sheet is swabbed with a 2 percent alcoholic solution of silvernitrate and allowed to dry. The sheet is exposed via a projectiontransparency to a tungsten source. The light striking the surface is Ifoot candle seconds. Subsequent to exposure, a .1 percent solution of2,2-dinapthyl-para-phenylenediamine is applied to the exposed sheet. Thesheet is washed with a thiourea stabilizer after a dense image isformed.

EXAMPLE IX A dispersion of 38 parts by weight of titanium dioxidepowder, (anatase form), 16 parts by weight of 30 percent by weightPliolite in toluene, three parts by weight sodium oxalate, three partsby weight of polystyrene, three parts by weight silver nitrate, 40 partsby weight toluene and 4 X grams of Phosphine R (C.I.46055) per gram ofoxide as a 2 percent weight alcoholic solution is ball-milled for 12hours. The dispersion is coated 3.0 grams/ft. (dry) on a 45 pound lowedto dark adapt for a period of 12 hours. The sheet is exposed to atungsten source with 100 foot candle seconds balling on the surface. Thelatent image is developed with an aqueous solution of an aminophenolreducing agent. The developed sheet is further washed to stabilize.

EXAMPLE X A dispersion of 38 parts by weight of titanium dioxide powder,(anatase form), 16 parts by weight of 30 percent by weight Pliolite intoluene, three parts by weight of polystyrene, 3 parts by weight silvernitrate, 40 parts by weight toluene and 4 X 10" grams of Phosphine R(C.I.46055) per gram of oxide as a 2 percent weight alcoholic solutionis ball-milled for 12 hours. The dispersion is coated 3.0 grams/ft.(dry) on a pound Crocker-Hamilton paper which had been subbed with a 0.2gram/ft. layer of cellulose acetate. The layer is dried and allowed todark adapt for a period of 12 hours. The sheet is exposed to a tungstensource with 100 foot candle seconds balling on the surface. The latentimage is developed with an aqueous solution of an aminophenol reducingagent. The developed sheet is further washed to stabilize.

EXAMPLE XI A dispersion of (42 parts by weight) zinc oxide and (threeparts by weight) sodium oxalate in (11 parts by weight) Pliolite, (23parts by weight) acetone and (24 parts by weight) toluene wasball-milled for 12 hours. This dispersion was coated 4 mils thick on aMylar support and dried at room temperature with a subsequentdark-adapting period of 12 hours. This dispersion was coated 4 milsthick on a Mylar support and dried at room temperature with a subsequentdark-adapting period of 12 hours. An image-forming layer containing Ipart by weight gold chloride, 24 parts by weight polyvinylpyrrolidoneand 75 parts by weight methanol was coated in the dark to 3 mils thickand allowed to air-dry in the dark. This sheet was exposed to a mercuryarc lamp (3,000 lumens) for 20 seconds with the formation of a latentimage (reduction of small amount of gold chloride to gold). The exposedsheet was dipped in a solution of hydroquinone with an immediate visualdevelopment of the image in the light-struck areas. This is an exampleof latent image formation by light with subsequent visual development ofthe latent image by an external reducing agent. The sheet was thenwashed to remove the unreacted image-forming material and water-solublebinder to give a stable sheet. A Mylar film support with the abovesystem gave similar results.

EXAMPLE XII The effect of the reducing agent in causing an increase inimage density for a given exposure is exemplified by the following TableI. In the runs of the Table, a l-watt projection lamp (500 lumens) wasused as the light source. In Runs 1 through 5 of Table I, the papercompositions were prepared in accordance with the procedure of Example Iwith modifications as to the photocatalyst and omission of reducingagent as indicated. The tabulation of values in the columns below thetime of exposure in seconds of Table I is the change in optical densityfrom unexposed to exposed, and the higher values are the most desirable.

TABLE I 1 Change in Optical Density=(O.D.Ex weO.D.

Exposure seconds Run Compositions 2.5 5 10 15 20 30 l Zinc oxide, silvernitrate .01 .02 .035 .055 .08 .13 .23 275 2 Zinc oxide, silver nitrate,sodium oxalate 0.55 .08 115 .24 355 50 3 Titanium dioxide, silvernitrate 025 .04 05 065 .08 11 18 .23 Titanium dioxide, silver nitrate,sodium oxalate .035 .05 .07 095 12 15 25 .37 5 (No photocatalyst),silver nitrate. sodium oxalate 0.00

1 Change in optical density for indicated exposures to tungsten lamp.

Crocker-Hamilton paper which had been subbed with a 0.2 gram/ft. layerof cellulose acetate. The layer is dried and al- I-Iaving described ourinvention, we claim: 1. A method for making a reproduction of aradiation image which comprises (1) providing a sheet comprising aninert carrier bearing (a) a solid photocatalyst phase comprising a metalcontaining substance activatable into transfer of electrons to anelectron acceptor by a wave length below 1 micron, and (b) a reduciblephase comprising an oxidizing agent which accepts electrons from saidphotocatalyst to form a free metal; (2) exposing said sheet to aradiation image to cause said photocatalyst to donate electrons to saidoxidizing agent to reduce a portion thereof to a free metal defining alatent image; and (3) post-exposure treating said sheet with a reducingagent reactable with the unreacted portion of said oxidizing agent inthe presence of said free metal whereby said latent image is developedto a visible image.

2. The method of claim 1 wherein said photocatalyst is at least onemember selected from the class consisting of zinc oxide and titaniumdioxide.

3. The method of claim 1 wherein said oxidizing agent is at least onemember selected from the class consisting of a gold salt and a silversalt.

4. The method of claim 1 wherein said reducing agent is at least onemember selected from the class consisting of a dihydric phenol and anaminophenol.

5. A method for making reproduction of a radiation image which comprises(1) providing a sheet comprising an inert carrier bearing (a) a solidphotocatalyst phase comprising a metal containing substance activatableinto transfer of elec- *trons to an electron acceptor by a wave lengthbelow 1 micron, (b) a reducible phase comprising oxidizing agent whichaccepts electrons from said photocatalyst to form a free metal, and (c)a solid oxidizable phase in non-reactive relationship with saidreducible phase, said oxidizable phase comprising a reducing agentcapable of donating electrons to said photocatalyst; (2) exposing saidsheet to a radiation image to cause said photocatalyst to donateelectrons to said oxidizing agent to reduce a portion thereof to a freemetal defining a latent image; and (3) post-exposure treating said sheetwith a second reducing agent reactable with the unreacted portion ofsaid oxidizing agent in the presence of said free metal whereby saidlatent image is developed to a visible image.

6. The method of claim 5 wherein said photocatalyst is at least onemember selected from the class consisting of zinc oxide and titaniumdioxide.

7. The method of claim 5 wherein said oxidizing agent is at least onemember selected from the class consisting of a gold salt and a silversalt.

8. The method of claim 5 wherein said reducing agent is at least onemember selected from the class consisting of a dihydric phenol and anaminophenol.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N a 6 5 383I Dated April ll. 1972 Inventofls) Joseph W. Shepard and Benjamin L.Shely It is certified that error appears in the above-identified patentand that said Letters Patent are hereby corrected as show-n below:

On the title page, under the right hand column, the phrase "3 Claims, NoDrawings" should read 8 Claims,

No Drawings I Col. 7, line 5, "absorption" should read adsorption Col.8, line 13, "side" should read site Col. 14, in Table I under heading2.5, Run No. 2 "0.55

should read .055

Signed and sealed this 5th day of September 1972.

(SEAL) Attest LDUARD M .FLETGHl-JH, JR

ROBERT GOTTSCHALK At 50 s ting; Offi ce r Commissioner of Patents 'ORMPO-1050 (10-69) USCOMM'DC 6O376-P69 U.Si GOVERNMENT PRINTING OFFICE:1959 0-366-31

2. The method of claim 1 wherein said photocatalyst is at least onemember selected from the class consisting of zinc oxide and titaniumdioxide.
 3. The method of claim 1 wherein said oxidizing agent is atleast one member selected from the class consisting of a gold salt and asilver salt.
 4. The method of claim 1 wherein said reducing agent is atleast one member selected from the class consisting of a dihydric phenoland an aminophenol.
 5. A method for making reproduction of a radiationimage which comprises (1) providing a sheet comprising an inert carrierbearing (a) a solid photocatalyst phase comprising a metal containingsubstance activatable into transfer of electrons to an electron acceptorby a wave length below 1 micron, (b) a reducible phase comprisingoxidizing agent which accepts electrons from said photocatalyst to forma free metal, and (c) a solid oxidizable phase in non-reactiverelationship with said reducible phase, said oxidizable phase comprisinga reducing agent capable of donating electrons to said photocatalyst;(2) exposing said sheet to a radiation image to cause said photocatalystto donate electrons to said oxidizing agent to reduce a portion thereofto a free metal defining a latent image; and (3) post-exposure treatingsaid sheet with a second reducing agent reactable with the unreactedportion of said oxidizing agent in the presence of said free metalwhereby said latent image is developed to a visible image.
 6. The methodof claim 5 wherein said photocatalyst is at least one member selectedfrom the class consisting of zinc oxide and titanium dioxide.
 7. Themethod of claim 5 wherein said oxidizing agent is at least one memberselected from the class consisting of a gold salt and a silver salt. 8.The method of claim 5 wherein said reducing agent is at least one memberselected from the class consisting of a dihydric phenol and anaminophenol.